Widespread resistance to antibiotics in current clinical use is increasing at an alarming rate. Novel approaches in antimicrobial therapy will be required in the near future to maintain control of infectious diseases. Virtually all organisms ranging from bacteria to humans produce an array of endogenous small cationic peptides as part of their innate defense systems. For the majority of these peptides that are linear (i.e., not crosslinked by disulfide bonds), such as magainins and cecropins, a common feature is their capacity to form an amphipathic alpja-helix (with polar and nonpolar groups on opposite faces of the helix), a structural feature believed to be important in their antimicrobial function as membrane-lytic agents. A massive effort over the past ten years has resulted in a better understanding of the molecular mechanism of these antimicrobial peptides and the production of more potent analogues. To date, however, only a few of these peptides have been tested clinically due to insufficient selectivity between target and host cells. We have developed a design for a new class of linear cationic antimicrobial peptides which form amphipathic beta- sheets rather than alpha-helices. We have demonstrated that peptides in this class possess superior selectivity in binding to the lipids contained in bacterial vs. mammalian plasma membranes and that peptides as short as nine residues are promising antimicrobial candidates. The specific aims for this project are to: 1) determine the antimicrobial and hemolytic activity of new peptide variants containing strategic alanine, proline, cyclohexylalanine and D-amino acid substitutions; 2) measure the ability of these peptides to induce leakage in and bind to lipid bilayers and membranes; 3) test for antiviral activity using two enveloped viruses, herpes simplex and influenza; and 4) test for antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermis, which are the most common causes of nosocomial skin infections in humans. This innovative project will address fundamental questions in peptide structure and function, and aid in identifying small and selective antimicrobial peptides that could produce leads for animal and clinical testing as topical agents. The project also will provide educational and research opportunities to undergraduates at our institution. With antibiotic resistance and viral diseases proliferating at an ever-increasing rate, this new class of linear amphipathic beta-sheet-forming antimicrobial peptides is certainly worthy of continued exploration. [unreadable] [unreadable] [unreadable]